Cellulosic fibers and fibrous articles and method of making same



United States PatentO a s 052 593 CELLULOSIC FIBERS AN,D FIBROUS ARTICLES AND METHOD OF MAKING SAME Orlando A. Battista, Drexel Hill, Pa., assignor to Ameri- 3,052,593 Patented Sept. 4, 1962 2 viscose process, do not exhibit this type of fibrillation. This lack of a fibrillating characteristics prevented the use of these conventional synthetic fibers in the manufacture of water-laid webs unless a binding material or substance Was incorporated either in the furnish or applied p 5 :5; x ggg sgg Phlladelphla a corporato the Water-laid web before removal from the collecting No Drawing. Filed Dec. 31, 1958, Ser. No. 784,033 Screensynfhetic P fibrs of this. tYPe 1180 are 13 m (CL 1 2 ..14 extremely difiicult to d1sperse In Water in the absence of dispersing agents. The inability to produce fibI'llS This invention relates to a new and novel synthetic 10 from conventional synthetic cellulosic fibers such as viscellulose fiber, method of making such fiber and prodcose rayons has restricted their use in forming water-laid ucts containing the fiber. webs to certain types of specialty papers.

Fibrous articles, such as certain types of non-Woven The principal purpose of the present invention is to fabrics and water-laid sheets, depend to a large extent provide a fibrillated synthetic cellulose fi ber. on an interlocking of the fibers and of fibrillae on the Another purpose of this invention is to provide a fibers for their physical properties such as strength, tear method for fibrillating synthetic cellnlosic fibers. and burst. The most widely used material which may be A further purpose of the invention is to provide waterclassed as a non-woven fabric is paper commonly formed laid fibrous sheets of the novel fibrillated synthetic cellufrom a furnish which contains the dispersed fibers. It lose fibers having physical properties far exceeding those is common knowledge that natural fibers such as wood of similar sheets of synthetic cellulosic fibers as formed pulp, cotton linters and the like when hydrated as by heretofore. beating and mixing in a conventional paper mill beater Another object of this invention is to provide strong, become fibrillated. Fibrillation as employed in the tough water-laid fibrous sheets composed of the novel paper-making art is obtained substantially by the beating fibrill-ated synthetic cellulose fibers with or without other or vigorous agitation of fibers in the presence of extremely synthetic fibers or natural fibers or mixtures thereof. large excess quantities of Water. This fibrillation desig- Other objects and advantages of the invention will be nates what might be termed a microscopic and submicroapparent from the description as follows. scopic progressive peeling of individual fibers along the The present invention contemplates subjecting synthetic surface and at the ends of the fiber bundles and this action cellulose fibers, such as regenerated cellulose fibers, to a is obtained Without chemically altering the fiber. It is closely controlled hydrolysis treatment followed by a vigcommon knowledge that fibrillation is an inherent characorous mechanical agitation of the treated fibers in a large teristic of the naturally occurring cellulose fibers. On excess amount of water to effect a fibrillation of the fibers the other hand, the synthetic cellulosic fibers, that is, fibers and subsequently separating the fibrilla-ted fibers fromformed by regenerating the cellulose from a collulosic the aqueous liquid. compound, for example, such as those produced by the A flow diagram of the process is as follows:

- Synthetic Cellulose Fibers i Controlled partial hydrolysis i Fibrillatable F"- Synthetic Cellulose Dry Fibers Fibers Dried Flbr-illatable Synthetic Cellulose Mechanical agitation or brushing in aqueous Brush in aqueous liquid Fibrillated Syncheci Cellulose Fibers Dried Fibrlli lated Synthetic Cellulose- Mix with water (with or without; other Mix with water (with or without other fibers) Sheet and dry Water-laid Product;

fibers) Fibers v l Mix; in water (winner without other sheet and dry fibers) if I waber-laid Product? urrnsh sheet and nit- For some time, various investigators in studying the structure of both native and regenerated cellulose have subjected cellulose fibers to a severe hydrolyzing treatment wherein the amorphous cellulosic material is removed and only a very fragile cellulosic skeleton remains. This residue or remaining portion of the fiber consists essentially of cellulose crystallites. In these investigations, a measured quantity of the fibers is transferred to a suitable acid solution and is maintained in the acid for varying periods of time. After the time period has elapsed, the material is thoroughly washed to remove the acid and may be subjected to subsequent tests. Generally, the acid solution is a 2.5 N hydrochloric acid solution maintained at about 105 C. which is the boiling point. The fibers are maintained in the boiling acid solution for about 15 minutes. This treatment removes the so-called amorphous cellulose and the residue consists of the cellulose crystallites recovered from the fibers. In my copending application Serial No. 636,483, filed January 28, 1957, now Patent No. 2,978,446, there is disclosed a method of preparing stable dispersions of level-off D.P. cellulose by subjecting cellulose crystallites in this form to a vigorous mechanical agitation in water. If the residue product ofithis hydrolysis treatment is subjected to a mild agitation, such as by means of a paddle stirrer, the fibrous material is merely broken into small particles which will settle like fine sand. The level-off DR of the cellulose from the regenerated cellulose fibers lies in the range of from about 20 to about 50. When native cellulosic fibers, on the other hand, are subjected to a like treatment, it is found that the level-off DR of native cellulose is in the range of from about 150 to about 300.

It has now been discovered that regenerated cellulose fibers may be partially hydrolyzed to render them satisfactory for use in conventional paper-making processes by subjecting the fibers to a closely regulated and controlled hydrolysis treatment without measurably decreasing the weight of the fibers so as to reduce the average basic DR of the cellulose in the partially hydrolyzed fiber to from about 20% to about 75% of the average basic DR of the cellulose in the parent fiber.

Any form of regenerated cellulose fiber may be subjected to the controlled hydrolysis to render the fibers suitable for the purpose of this invention The specific conditions for satisfactory hydrolysis are dependent upon the specific cellulose fine structure of any particular fiber and are chosen to elfect a limited cutting of the cellulose chains which run continuously through the amorphous areas of the respective fine structure. In general, there is no measurable weight loss and, in any event, the weight loss should not exceed about 1%. As is well known, the average basic DR of regenerated cellulose is in the range of about 350 to about 550. The hydrolysis treatment must be sufiicient to lower the average basic DR of the cellulose in the fiber to a value within the range of about 20% to about 75 of the origin-a1 D.P. If the hydrolysis treatment is prolonged or sufficiently severe to reduce the average basic DR of the cellulose below about 20% of its value in the parent fiber, then the fiberis weakened excessively and the partially hydrolyzed fiber will disintegrate into a powder upon me chanical' agitation, thereby preventing the manufacture of water-laid sheets. If, on the other hand, the hydrolysis is not sufiicient to reduce the average basic D.P. below about 75 of its value in the parent fiber, then upon subsequent mechanical treatment, the partially hydrolyzed fiber will not fibrillate to an extent which permits the manufacture of a satisfactory water-laid sheet.

- The hydrolysis treatment may be satisfactorily carried out by subjecting the fibers to the action of a dilute acid solution maintained at a temperature up to about 95 C. under atmospheric pressure or higher temperatures may be employed when the treatment is carried out in a closed vessel under pressure. Convenient and economiically feasible treating solutions may be aqueous solutions of sulfuric acid having a concentration up to about 10% acid by weight and hydrochloric acid solutions containing up to about 8.5% hydrochloric acid. As is apparent, the time required will be dependent upon the acid c ncentration and the temperature maintained during the hydrolysis treatment. Because it is possible to utilize higher temperatures when the treating liquid is under pressure, the concentration of acid may be lowered sub stantially.

Several specific types of regenerated cellulose fibers are commercially manufactured and the specific conditions for satisfactory hydrolysis in accordance with the present invention will be dependent upon the nature of fine structure of the specific fiber. For example, conventional viscose rayon fiber for ordinary textile purposes consist of a core and rather thin skin. The relative proportions of skin to core vary with different types of viscose rayon and are dictated by the desired end use. For tire cord purposes, present commercial viscose rayon consists of fibers having from 75 to or up to skin with the remainder core. These different forms or grades respond somewhat differently to hydrolysis and the specific hydrolysis conditions will accordingly be esstablished based upon the specific characteristics of the fiber. In general, the all skin type fiber or the fiber which has a very large proportion of skin as compared to core will require somewhat more drastic hydrolysis conditions than are required for the usual textile grades of viscose rayon which have a very thin skin.

In general, the hydrolyzing conditions for any specific fiber will be satisfactory for fibers having diameters up to about 40 or more microns. It has been found, however, that there is a gradual decrease in the length of the fibrils which are formed on treated fibers as the diameter of the fiber increases. The fibers may be cut to the desired length prior to subjecting them to the controlled hydrolysis or the fibers subjected to this treatment may be of considerable length as compared to natural fibers and cut to length after the treatment as in a paper mill beater.

Samples of commercial viscose rayon staple fiber having a relatively thin skin with respect to core may be satisfactorily treated under mild or severe hydrolyzing conditions. Because of the ease with which this type of fiber is hydrolyzed, the milder conditions are preferred. The length of the fiber may be from about 2 millimeters to as high as of an inch or greater and the diameter of the fibers may vary up to about 40 microns or more. Sulfuric acid solutions containing up to about 10% acid are satisfactory and the temperature of the acid solution may vary up to about 95 C. It is quite apparent that the time required will vary inversely with the concentration of the acid and inversely with the temperature. In determining the fibrillating characteristics, it has been found that a 20 minute treatment of a fiber in a standard Waring Blendor will produce about the same characteristics as a 2 hour brushing in a laboratory type Valley beater. Standard laboratory Lightnin mixers and Cowles dissolver or hydropulper blades attached to a kitchen-type Dormeyer mixer are also satisfactory for determining the fibrillating characteristics of fibers but require about 2 hour mixing periods.

In the following examples, the fibrillating characteristics of regenerated cellulose fibers treated with dilute acid solutions were determined by subjecting the treated fibers to a brushing action for 20 minutes in the Waring Blendor at a 1.5% consistency. The dry regenerated cellulose fibers had a diameter of about 12 microns and were about /2 inch inlength.

In a first group of tests, samples of a commercial textile grade of viscose rayon having a thin skin and a crenulated cross-section were subjected to the action of dilute sulfuric acid under various conditions. After each specific treatment, a portion of the sample of the treated fibers was used to determine the average basic DR of the cellulose and another portion subjected to the fibril lation test.

The data in Table I illustrates the fibrillating characteristics as related to the average basic D.P. of the treated fibers. In this particular regenerated cellulose fiber, it will be noted that when the average basic D.P. has been reduced below the limit hereinbefore set forth, the treated fiber when beaten in water breaks up into fine particles because it has been weakened to too great an extent. Within the average basic D.P. range as set forth hereinabove, the physical characteristics of the fiber before treatment, such as the tenacity or tensile strength and percent elongation, have been decreased to some extent by the controlled hydrolysis and the treated fibers have excellent fibrillating characteristics. Within this range, there is substantially no measurable weight loss whereas in the case of the treated fiber having a very low average basic D.P., there is a measurable decrease in weight. On the other hand, where the hydrolysis treatment has not been sufiicient to lower the average basic D.P. to a value Within the stated range, the fiber will not fibrillate.

TABLE I Variation of Average Basic D.P. and Fibrillation With Hydrolysis Treatment Excellent. D

0. Very poor; powdered.

In further similar tests, samples of another commercial viscose rayon staple wherein the fibers consisted of at least 75% to 100% skin and had a smooth exterior surface were subjected to hydrolysis by the use of 8.3% hydrochloric acid solutions. The fibers were subjected to the treatment at various temperatures and for various periods of time. From the data in Table II, it will be noted that here again fibrillating characteristics are obtained when the average basic D.P. of the cellulose in the treated fibers falls within the stated range of about 94 to about 350 (20% to 75% of 470) for this type of rayon. Although the sample which showed an average basic D.P. of 75 after treatment showed good fibrillating characteristics at the initiation of the beating in water, the hydrolysis had been so severe that the fibers were weakened excessively and were very rapidly (4 to 5 min.) reduced to a powdery mass upon mechanical agitation. The beaten mass was incapable of forming a water-laid web.

TABLE 11 Variation of Average Basic D.P. and Fibrillation With Hydrolysis Treatment The controlled hydrolysis treatment as stated above may also be carried out at elevated temperatures under pressure and it is thereby possible to substantially reduce the acid requirements. As noted in Table III, samples of the first-mentioned viscose rayon staple fibers were subjected to treatment with sulfuric acid solutions of lower concentrations at a temperature of 120 C. While maintaining the mass under a gauge pressure of 10 psi. Various concentrations of acid were employed for different time periods. Upon comparison with the data of Table I, it will be found that appreciably less acid is required and the time period may be shortened to produce fibers having satisfactory fibrillating characteristics. Products wherein the average basic D.P. has been reduced below about 74 do not possess fibrillating char acteristics but break up into very short particles (of the order of 1 mm. and less) when subjected to the 20 minute agitation in a Waring Blendor. It will be noted that the sample subjected to the action of the 0.2% sulfuric acid solution for minutes had the same average basic D.P. as that of the sample subjected to .a 10% sulfuric acid solution at 80 C. at atmospheric pressure for 10 minutes (sample III, Table I). These samples, on comparison, revealed identical strengths, fibrillating characteristics and paper sheet forming characteristics.

TABLE III Eflect of Pressure Hydrolysis Conditions on Average 5 Basic D.P. and Fibrillation Hydrolysis Time of Average Fibrillation Run treatment treatbasic after beating No. 120 O. 10 psi. merit, P. minutes 1 0.5% H2504 30 70 None.

2 3 0% HlSO4 30 50 Do.

3 1.5% H280 20 50 Do.

4..-" 0.1% H250 15 240 Many tiny fibrils.

5 0.2% HZSO; 15 160 Excellent.

TABLE IV Effect of Pressure Hydrolysis Conditions on Average Basic D. P. and Fibrillation Hydrolysis Time of Average Run treatment treatbasic Fibrillation No. 120 0. 10 p.s.i. merit, D.P. after beating minutes Numerous tiny fibrils. Long fibrils produced.

The foregoing hydrolysis treatments are not the exclusive means for rendering regenerated cellulose fibers fibrillatable as defined herein but are merely illustrative. Other means are entirely satisfactory. For example, a polyvalent metal ion may be included as a catalyst and may allow the use of lower acid concentrations and shorter treating periods. Thus a three minute treatment of the fibers in a 2% sulfuric acid solution containing 1% ferric chloride at 80 C. is equivalent to a 10 minute treatment in a 10% sulfuric acid solution at 80 C.

The controlled hydrolysis treatment which is suflicient to render the normally non-fibrillatable fibers readily fibrillatable under normal paper-making conditions does not drastically reduce the physical characteristics of the fiber. This is demonstrated by a comparison of the 75 single fiber characteristics of the control samples of the 7 two types of rayon staple fibers mentioned hereinbefore and of samples of both of these types of fibers which have been subjected to both the low temperature and the high temperature controlled hydrolysis. The hydrolysis treatment as set forth in Table V has been selected as a more or less optimum hydrolysis treatment for the two specific types of fibers.

TABLE V Comparison of Single Fiber Strengths of Control and Hydrolyzed Fibers Avg. Avg. Aver- Fiber type Hydrolysis treatment tenacit percent age basic -l elong- D. P. den.) ation Thin skin 3. OS 19. 6 380 Do 10 min. in 10% H2804 at 80 C 2. 33 14. 6 160 D 15 min. in 0.2% H 504 at 120 C, p.s.i 2. 57 16. 9 160 Thick skin-" 3. 93 29. 2 470 D0 30 min. in 2.5N HCl at 55 C-- 2. 55 20. 2 240 D0 40 min. in 2.5N HCl at 55 C 2. 71 21. 3 200 It has been well known in the art that viscose rayon does not respond to the conventional paper-making process.- For example, in a paper by May, Isenberg and McLeod, published in vol. 142, Paper Trade Journal, January 6, 1958, pages 3640, it is stated that regenerated cellulose fibers lack the fibrilated structure of natural cellulose fibers and consequently beating does not develop fiber/fiber bonding. Furthermore, many types of rayon, regardless of fiber length or size, will not disperse in Water in the absence of added dispersing agents. Thus, a sample of the first mentioned commercial viscose rayon staple having a diameter of about 12 microns and having a length of about 0.5 inch were placed in a TAPPI standard beater at a 0.6% consistency and containing about 150 grams of fiber. Circulation was finally arrested by an agglomeration of the fibers and it was impossible to form hand sheets from such rayon fibers. This is typical of conventional types of viscose rayon fibers. On the other hand, fibers subjected to the controlled hydrolysis treatments as described herein are readily dispersed in and fibrillated in this standard type of beater. The treated fibers formed as described herein may also be mixed with natural paper-making fibers or other synthetic fibers in a conventional paper mill beater and may be handled and processed in accord with conventional paper-making methods. The products exhibit an unusually uniform texture whether the fiber consists entirely of the partially hydrolyzed fiber formed as described herein or when blended or mixed with nat- Ural paper-making fibers or other synthetic fibers. One particularly advantageous application of'the treated fibers includes the mixing of fibers prepared according to the present invention with fibers which normally produce a rather weak wet strength paper such as newsprint web. The treated regenerated cellulose fibers may be of a longer length and of various thicknesses to contribute an appreciably higher Wet strength as well as a higher dry strength.

The manufacture of the fibers may involve only the controlled hydrolysis treatment and subsequent washing and drying of the fibers or may include a washing of the treated fibers followed by a fibrillation treatment and a final drying step. Where the fibers have been dried after the controlled hydrolysis treatment, they are subsequently handled by the same method which is used in producing water-laid webs from a refined paper pulp; that is, the fibers are subjected to a brushing action for a period of from '15 minutes to 3 hours. Where the fibers after controlled hydrolysis are washed and fibrillated as by the action of a paper mill beater and then dried, no additional brushing is required. The typical fibrillae of the dry, fibrillated fiber are developed by a mere mixing in water. In the use of the dry, fibrillated. fiber, it is merely necessary to disperse the fibers in water by any of the conventional mixing devices, such as by brushing in a paper mill heater or by mixing with a Cowles stirrer and then form the furnish which is passed directly to the head box of the paper machine. The fibers are then sheeted to form a web in exactly the same manner that normal paper-making fibers are converted into a web. The thickness of the sheeted fibers is regulated to form any desired grade or thickness of fibrous web. The web may be subjected to calendering rolls, etc., and dried in accordance with conventional paper-making processes.

Where the fibers treated in accordance with the present invention are to be mixed or blended with other fibers, it is preferable to separately disperse the respective fibers in Water and subject the fibers to the required action separately to develop the fibrillate before mixing the dispersions. For example, if fibers of the present invention and normal paper-making fibers are to be mixed or blended, it is preferable to separately subject the different types of fibers to their individual optimum fibrillating treatments as by beating or brushing because excessive beating will remove some of the fibrillae. Thus, where optimum beating times for different fibers differ, the separate and independent beatings may be regulated to obtain maximum fibrillation of the respective types of fibers.

As is well known, ordinary rayons of the types described hereinbefore may be converted to water-laid webs by very careful manual manipulation to form a paper-like sheet. Because these regenerated cellulose fibers do not have a fibrillar structure, the dried sheets have such low strengths that the conventional tensile tests, burst tests and tear tests as applied the sheet cannot be measured. The slightest application of force pulls the fibers apart.

Satisfactory water-laid webs of the fibers of this invention may be formed by any of several conventional methods. For example, manufacture of paper may be illustrated by standard paper laboratory procedures which involve the use of a TAPPI standard beater and the preparation of handsheets with a Noble and Wood screen. In the specific samples which are enumerated in the table which follows, grams of fiber were dispersed in the TAPPI standard beater at a consistency of 0.6%. In the table, the lever weight refers to the weight applied to the lever which moves the bedplate to contact the beater roll. The standard weight in beating wood pulps is 5500 grams. By the use of the low weights on the lever, the fibers are subjected to a brushing action rather than a beating action. The Weight in pounds of the samples refers to the calculated Weight for a ream of 500 sheets 25 inches by 40 inches.

50X Mullen burst in p.s.i.

h M f T e ullen burst actor Ream weight in pounds 71.1 X Elmendorf tear in grams f The tear actor Ream weight in pounds 21,500 lbs. Ream weight lbs.

47,400X p Ream weight in lbs.

where p is the breaking load of a 15 mm. strip in kilograms.

Table VI Beating Length, Diam- Rayon Mixture Weight, Mullen Tear Tensile Fiber in. eter, lb. burst factor strength,

denier factor meters Lever Time, Lever Time, weight, min. weight, min.

gm. gm.

CTS 0.5 1. 227 240 HT 0.25 3.0 1, 360 15 63. 4 3 78 552 Woodpulp A. 6,500 21 58. 5 32 61 5, 660 HTS plus 90% A.. 0.25 3.0 227 20 227 30 56. 7 30 83 5, 620 20% HTS plus 80% A 0.25 3.0 227 30 227 30 83.2 34 115 6,060 50% HTS plus 50% A 0.25 3.0 227 45 227 30 59.3 20 138 3,070 20% I-ITS plus 80% A 0. 50 1. 5 227 20 227 30 62. 9 29 83 4, 610 Woodpulp B 227 57. 7 56 76 7,740 HTS plus 80% B 0.25 3.0 227 60 227 58. 9 42 94 6, 460 20% TTS plus 80% 0.50 1. 5 227 60 227 30 56.1 34 145 6, 500 50% HT S-2 0.50 1. 5} 1,360 45 64. 3 4 75 915 50% TTS 0.50 1. 5

1 Circulation in the beater stopped by agglomeration of fibers preventing the formation of handsheets.

Table legends:

CTS-Control (untreated) thin skin rayon.

TTS-Partially hydrolized thick skin rayon, 1 hr. in 2.5 N HCl at 50 C.

Woodpulp A-Commercial western hemlock bleached sulfite pulp.

Woodpulp B-Mixed hardwood bleached neutral sulfite semi-chemical pulp.

It is quite clear from the foregoing table that conventional textile grades of viscose rayon do not respond to commercial paper-making techniques. The other examples have been selected, not to indicate paper having outstanding characteristics but to illustrate the various modifications which may be eifected by blending fibers of the present invention with natural paper-making fibers. For example, it will be noted that with respect to the specific rayon fibers employed in the examples, the paper possessed about the same tear factor as wood pulp papers although the burst factor and tensile strengths were very low. On the other hand, the papers formed from blends or mixtures do not possess characteristics which are averages or sums based on the properties of the individual fibers of the mixture. It will be noted that by the use of various proportions of the partially hydrolyzed rayon with wood pulps, the burst factor or the tear factor or the tensile strength of the papers may be selectively altered. Thus, by the addition of 10% of the partially hydrolyzed rayon to Wood pulp, the tear factor may be increased by about 35% with no appreciable alteration of the burst factor and tensile strength. Or the tear factor may be doubled without an appreciable change in the burst factor and with less than a 10% change in the tensile strength by the use of 20% of the treated rayon.

This data is presented merely as illustrative and representative of the alteration or modification in paper characteristics which may be effected by the use of the partially hydrolyzed fibers of this invention.

As pointed out hereinbefore, a 20 minute beating or mixing in a Waring Blender is approximately equivalent to a 2 hour brushing in the standard TAPPI Valley Beater. In the examples reported in the table which follows, commercial thin skin rayon fibers and thick skin rayon fibers as described above were subjected to such brushing after partial hydrolysis. The partial hydrolysis consisted of treating the fibers for 10 minutes in a 10% sulfuric acid solution at 80 C. The thick skin rayon fibers were treated for 20 minutes in a 10% sulfuric acid solution at 80 C. Both types of fibers were A inch in length. The thin skin fibers were of a 1.5 denier size (about 12.5 micron diameter) and the thick skin fibers Were of a 0.5 denier size (about 6-7 micron diameter). In each instance, the fiber or mixture of rayon fibers and wood pulp Was beaten or brushed in a standard Waring Blender for 20 minutes at a 1.2% consistency and handsheets were prepared from the slurry by the standard paper technique using a Noble and Wood screen. In one instance, the fiber was pounded in a mortar before being subjected to the brushing. The data is illustrative of variations obtainable by the use of the fibers of this invention.

TABLE VII Weight Mullen Tear Tensile Fiber lbs burst factor strength,

factor meters 34. 2 10 100 1,075 34. 2 10 116 1,133 S 41. 2 18 128 2, 640 HTS 10% pulp C 31.7 10 155 839 80% HTS 20% pulp C 44. 3 9 273 1,038 70% HTS 30% pulp O 36.2 11 293 1,668 pulp O 39 17 66 3, 200

Norr..HTSPartially hydrolyzed thin skin rayon, 1.5 denier size.

lTS- -Partia1ly hydrolyzed thick skin rayon, 0.5 denier size. Chemipulp, commercial newsprint grade pulp.

1 Sample pounded in mortar prior to brushing.

Pulp O- The data illustrate-s that the treatment and size of the fibers may be selected to impart desired characteristics to the water-laid web. Where the fibers Were subjected to a pounding in a mortar which is somewhat comparable to a grinding or crushing, a higher tear factor and tensile strength is noted. Finer fiber size or small diameter fibers form paper having higher strength, burst and tear properties. The blending or mixing of fibers of the present invention and natural paper-making fibers results in small changes in the bursting strength but appreciable increases in the tear factor as compared to papers formed entirely 3; the fibers of this invention and of natural paper-making ers.

All of the foregoing data on the properties of waterlaid Webs refers entirely to the properties of Webs formed from a dispersion of the fibers in Water without the presence of other substances normally used in the manufacture of water-laid Webs. Sizing materials, fillers, binders, substances adapted to improve the wet strength and any other desired substances as normally used in the paper and pulp industry and in the manufacture of non- Woven fabrics may be incorporated in the fiber slurry or may be incorporated in the water-laid web. It will also be noted that in the standard paper laboratory methods of forming handsheets, no calendering of the web is employed. The strength characteristics of Webs formed with fibers of this invention are improved by a calendering in the same manner as Webs formed of natural paper-making fibers. For example, synthetic resins such as polyoleiins, acrylics, urea-formaldehyde resins, inelamine-formaldchyde resins, etc. may be applied at any suitable stage in the manufacture of the web or sheet.

Thus, melamine-formaldehyde resins may be utiiized to improve the wet strength of the sheet. The sheet may be impregnated with a fireproofing agent before final drying. Furthermore, although the foregoing description has been somewhat specific in reference to the production of paper, the collecting surface may be of any desired shape and form and the thickness of the web may be such as to form a non-woven textile of the nature of felt. The web sheet may be transferred to any desired mold and finished by pressing and drying in such mold.

The use of conventional commercial paper-making additives is illustrated by the examples reported in the table which follows. Commercial thin skin rayon fibers having a diameter of about 12.5 microns and having a length of 4 inch were subjected to treatment with a sulfuric acid solution at 80 C. for 10 minutes. After washing and drying, the fibers (HR) were then brushed in a Waring Blender for minutes at a 1.2% consistency and handsheets were prepared using a Noble and Wood screen. In certain instances, a commercial cationic starch derivative designated as Cato 8 was added in the Waring Blendor. Cato 8 is manufactured by National Starch Products, Inc., as a wet-end additive in paper-making adapted to improve the strength factors of paper. The data is representative and illustrates that the usual paper-making additives and impregnants effect the same types of improvements in products formed from the fibers of this invention as are obtained in the use of natural paperrnaking fibers.

The foregoing examples have included mixtures of fibers of the present invention and natural paper-making fibers or wood pulp fibers. One of the highly desirable characteristics of the fibers of the present invention is that the fibers may be of substantially identical diameter and length whereas the naturally occurring fiber-s in fact are in the nature of bundles of individual fibers and are not all of the same length. As a result, accurate desired modifications of water-laid webs may be effected by the use of fibers of definite and uniform dimensions. Although the examples illustrate merely mixtures of two different types of rayon which have been partially hydrolyzed as described herein and mixtures of these fibers with wood pulp fibers, any other desired type of papermaking fiber or any other type of fiber may be mixed with the fibers of the present invention. Rayon fibers which are commercially available for a wide variety of textile uses, as pointed out above, are not adapted in themselves for the manufacture of paper. However, by mixing or blending the fibers of the present invention 'Wtih such non-fibrillating fibers, satisfactory papers and water-laid webs may be produced. The fibers of this invention may also be mixed with other synthetic and natural fibers such as cotton, glass fibers, wool fibers, polyester fibers, cellulose acetate fibers, nylon fibers and other vegetable fibers. In forming papers or Water-laid webs, the fibers of thepresent invention may be of any desired length and will satisfactorily bond together other fibers which do not fibrillate.

As pointed out hereinbefore, fibrillatable regenerated cellulose fibers which are satisfactory for the manufacture of water-laid webs in accordance with the present invention are defined herein as partially hydrolyzed regenerated cellulose fibers wherein the average basic DR of the cellulose lies within the'range of from about 20% to about 75% of the average basic DR of the parent fiber. These fibers are further characterized by their fibrillating property which results in the formation of water-laid webs having certain minimum strength characteristics. The fibrillating property is measured by subjecting the fibers to a brushing treatment, forming a water-laid web in accordance with standard paper laboratory techniques and measuring the strength and tear factor of the water-laid sheet. Since a 20 minute beating in a standard 1 quart size Waring Blendor is the substantial equivalent of the normal 2 hour brushing in the standard Valley beater, it is preferred to express the fibrillating characteristics in terms of the treatment in the Waring Blendor which permits the use of smaller samples of the fibers and is a substantial reduction in the brushing or heating time. The fibrillating regenerated cellulose fibers as contemplated by the present invention when beaten in the standard Waring Blendor for 20 minutes at a 1.2 consistency, converted to handsheets on the standard Noble and Wood screen and dried without calendering form a sheet having a tensile strength expressed as breaking length of at least 400 meters and a tear factor of at least 50. As pointed out hereinbefore, rayon fibers which have not been partially hydrolyzed when subjected to the same test conditions form sheets which do not have a measurable tensile strength and a measurable tear factor. The magnitude of the minimum strength characteristics for paper sheet formed from the fibers of this invention may be visualized by comparison With the similar characteristics of ordinary newsprint. Normal newsprint papers have a tensile strength of about 3000 meters and a tear factor of about 47 in the machine direction of the web and a tensile strength of about 1400 meters and a tear factor of about 53 in a direction transverse to the machine direction.

The average basic DR of the cellulose as referred to herein and in the claims is based upon methods as described in the literature. For average basic D.P.s above 300, the method employed is that published by Orlando A. Battista, Molecular Weight of Cellulose, Ind. Eng. Chem., Anal. Ed, 16, 35l-354 (1944). For the average basic D.P.s below 300, the method employed is that published by Orlando A. Battista et al., Level-Off Degree of Polymerization, Ind. Eng. Chem., 48, 333-335 (1956).

Many different embodiments of the invention will be apparent and obvious to those skilled in the art and may be made Without departing from the spirit and scope of the invention. It is to be understood that the foregoing specific embodiments are included merely as illustrative and are not intended as limitations.

I claim:

1. A water-laid web comprising felted, water fibrillated, partially hydrolyzed regenerated cellulose fibers, the cellulose of the partially hydrolyzed fibers having an average basic D.P. within the range of from about 20% to about 75% of the original average basic D.P. of the cellulose of parent regenerated cellulose fibers subjected to a hydrolysis treatment and the partially hydrolyzed fibers being characterized by having substantially the same weight as the parent fibers and by forming a standard hand sheet having a tensile strength of at least 400 meters and a tear factor of at least about 50 from a slurry formed by beating the partially hydrolyzed fibers in water for 20 minutes in a standard Waring Blendor at a 1.2% consistency.

2. A water-laid web comprising a felted mixture of water-fibrillated, partially hydrolyzed regenerated cellulose fibers and other fibers, the cellulose of the partially hydrolyzed regenerated cellulose fibers having an average basic D.P. within the range of from about 20% to about 75 of the original average basic D.P. of the cellulose of parent regenerated cellulose fibers subjected to a hydrolysis treatment and the partially hydrolyzed fibers being characterized by having substantially the same weight as the parent fibers and by forming a standard hand sheet having a tensile strength of at least 400 meters and a tear factor of at least about 50 from a slurry formed by 13 beating the partially hydrolyzed fibers for minutes in a standard Waring Blendor at a 1.2% consistency.

3. A water-laid web as defined in claim 2 wherein the other fibers are natural paper-making fibers.

4. A water-laid web as defined in claim 2 wherein the other fibers are synthetic fibers.

5. A water-laid web as defined in claim 2 wherein the other fibers are non-fibrillated regenerated cellulose fibers.

6. As a new article of manufacture, paper comprising felted, water-fibrillated, partially hydrolyzed regenerated cellulose fibers the cellulose of the partially hydrolyzed fibers being characterized by having an average basic D.P. within the range of from about 20% to about 75% of the original average basic D.P. of the cellulose of parent regenerated cellulose fibers subjected to a hydrolysis treatment and the partially hydrolyzed fibers being characterized by having substantially the same Weight as the parent fibers and by forming a standard hand sheet having a tensile strength of at least 400 meters and a tear factor of at least about 50 from a slurry formed by beating the partially hydrolyzed fibers in water for 20 minutes in a standard Waring Blendor at a 1.2% consistency.

7. As a new article of manufacture, paper wherein all of the fibers are water-fibrillated, partially hydrolyzed regenerated cellulose fibers, the cellulose of the partially hydrolyzed fibers being characterized by having an average basic D.P. within the range of from about 20% to about 75% of the original average basis D.P. of the cellulose of parent regenerated cellulose fibers subjected to a hydrolysis treatment and the partially hydrolyzed fibers being characterized by having substantially the same weight as the parent fibers and by forming a standard hand sheet having a tensile strength of at least 400 meters and a tear factor of at least about 50 from a slurry formed by heating the partially hydrolyzed fibers in water for 20 minutes in a standard Waring Blendor at a 1.2% consistency.

8. The method of forming water-laid fibrous webs which comprises subjecting regenerated cellulose fibers to a hydrolysis treatment until the average basic D.P. of the cellulose has been reduced to between about 20% and about 75% of the original average basic D.P. of the cellulose of the parent regenerated cellulose fibers without substantially reducing the weight of the regenerated cellulose fibers, brushing the treated regenerated cellulose fibers in water, sheeting the brushed fibers to form a waterlaid web and drying the water-laid web.

9. The method of forming water-laid fibrous webs which com-prises subjecting regenerated cellulose fibers to a hydrolysis treatment until the average basic D.P. of the cellulose has been reduced to between about 20% and about 75 of the original average basic D.P. of the cellulose of the parent regenerated cellulose fibers without substantially reducing the Weight of the regenerated cellulose fibers, brushing the treated regenerated cellulose fibers in water to form a slurry, mixing with the slurry other fibers, sheeting the mixture of fibers to form a waterlaid web and drying the Water-laid web.

10. The method as defined in claim 9 wherein the added other fibers are natural paper-making fibers.

11. The method as defined in claim 9 wherein the added other fibers are synthetic fibers.

12. The method of forming water-laid fibrous webs which comprises subjecting regenerated cellulose fibers to a hydrolysis treatment until the average basic D.P. of the cellulose has been reduced to between about 20% and about 75 of the original average basic D.P. of the cellulose of the parent regenerated cellulose fibers without substantially reducing the weight of the regenerated cellulose fibers, forming a mixture of the partially hydrolyzed regenerated cellulose fibers, other fibers and water, brushing the mixture of the partially hydrolyzed regenerated cellulose fibers and of other fibers in Water, sheeting the mixture of fibers to form a water-laid Web and drying the Water-laid web.

13. The method of forming water-laid fibrous Webs which comprises subjecting regenerated cellulose fibers to a hydrolysis treatment until the average basic D.P. of the cellulose has been reduced to between about 20% and about of the original average basic D.P. of the cellulose of the parent regenerated cellulose fibers without substantially reducing the weightof the regenerated cellulose fibers, brushing the treated regenerated cellulose fibers in Water to form a slurry, brushing natural papermaking fibers in water to form a second slurry, mixing the slurries, sheeting the mixture of brushed fibers to form a water-laid web and drying the water-laid web.

14. In a method of forming water-fibrillatable regenerated cellulose fibers, the step which comprises subjecting regenerated cellulose fibers to a hydrolysis treatment until the average basic D.P. of the cellulose has been reduced to between about 20% and about 75% of the original average basic D.P. of the cellulose of the parent regenerated cellulose fibers without substantially reducing the weight of the regenerated cellulose fibers.

15. In a method of forming regenerated cellulose fibers which fibrillate when mixed in water, the steps which comprise subjecting regenerated cellulose fibers to a hydrolysis treatment until the average basic D.P. of the cellulose has been reduced to between about 20% and 75 of the original average basic D.P. of the cellulose of the parent regenerated cellulose fibers without substantially reducing the weight of the regenerated cellulose fibers, brushing the treated regenerated cellulose fibers in water, separating the brushed, treated regenerated cellulose from the water and drying the regenerated cellulose fibers.

16. The steps in the method of forming water fibrillatable regenerated cellulose fibers as defined in claim 15 wherein the hydrolysis treatment comprise subjecting the regenerated cellulose fibers to dilute sulfuric acid.

17. The steps in the method of forming water fibrillatable regenerated cellulose fibers as defined in claim 15 wherein the hydrolysis treatment comprises subjecting the regenerated cellulose fibers to dilute hydrochloric acid.

18. As a new article of manufacture, Water fibrillated, partially hydrolyzed regenerated cellulose fibers, the cellulose of the partially hydrolyzed fibers having an average basic D.P. within the range of from about 20% to about 75% of the average basic D.P. of the cellulose of parent regenerated cellulose fibers subjected to a hydrolysis treatment and the partially hydrolyzed fibers being characterized by having substantially the same weight as the parent fibers, by fibrillating when mixed with water and by forming a standard hand sheet having a tensile strength of at least 400 meters and a tear factor of at least about 50 from a slurry formed by brushing the partially hydrolyzed fibers in water for 2 hours in a standard Valley beater at a 1.2% consistency.

References Cited in the file of this patent UNITED STATES PATENTS 2,810,646 Wooding et al. Oct. 22, 1957 2,930,106 Wrotnowski Mar. 29, 1960 FOREIGN PATENTS 474,414 Italy Sept. 23, 1952 OTHER REFERENCES Textile Research Journal, vol. 27, pp. 827-829 (October 1957) Battista: Ind. Eng. Chem., vol. 48, pages 333-335 (1956) Leveling Off Degree of Polymerization.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,052,593 September 4 1962 Orlando A0 Battista It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 34, for "collu'losic" read cellulosic 5 column 2, line 2, for "characteristics" read characteristic column 4, line 13 for "of" read or column 8 line 35, after "applied." insert to column 9 Table VI in the footnote to the table, for "Table legends" read Table legend column 10, TABLE VII column 1, line 2 thereof for HTS read HTS column 13 line 29,, for "basis" read basic column 14 line- 29, for "75 read 75% ---'5 line 34, after "cellulose" insert fibers line 38 for "comprise" read comprises Signed and sealed this. 1st day of January 1963.,

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents 

1. A WATER-LAID WEB COMPRISING FELTED, WATER FIBRILLATED, PARTIALLY HYDROLYZED REGENERATED CELLULOSE FIBERS, THE CELLULOSE OF THE PARTIALLY HYDROLYZED FIBERS HAVING AN AVERAGE BASIC D.P. WITHIN THE RANGE OF FROM ABOUT 20% TO ABOUT 75% OF THE ORIGINAL AVERAGE BASIC D.P. OF THE CELLULOSE OF PARENT REGENERATED CELLULOSE FIBERS SUBJECTED TO A HYDROLYSIS TREATMENT AND THE PARTIALLY HYDROYLZED FIBERS BEING CHARACTERIZED BY HAVING SUBSTANTIALLY THE SAME WEIGHT AS THE PARENT FIBERS AND BY FORMING A STANDARD HAND SHEET HAVING A TENSILE STRENGTH OF AT LEAST 400 METERS AND A TEAR FACTOR OF A LEAST ABOUT 50 FROM A SLURRY FORMED BY BEATING THE PARTIALLY HYDROLYZED FIBERS IN WATER FOR 20 MINUTES IN A STANDARD WARING BLENDOR AT A 1.2% CONSISTENCY. 